Chemically crimping nylon fibers through formation of disulfide bonds therein



United States Patent 3,331,656 CHEMICALLY CRIMPING NYLON FIBERS THROUGH FORMATION OF DISULFIDE BONDS THEREIN Stephen Desiderius Bruck, Bethesda, Md., assignor to the United States of America as represented by the Secretary of Commerce No Drawing. Filed Nov. 22, 1961, Ser. No. 154,371 3 Claims. (Cl. 8-1155) This invention relates to crimped nylon fibers and also to a chemical procedure for crimping nylon fibers.

Filaments made from various synthetic linear polyamides (generically known as nylon) have come into widespread commercial use for the fiber basis of numerous textile materials- Such filamentary polyamides (nylon) form a unitary chemically related class to which the practice of the instant invention is particularly adapted, regardless whether the specific polyamide has been formed by condensation of a diamine with a dicarboxylic acid, e.g., hexamethylenediamine and adipic acid (nylon- 66), by self-condensation of a l-actam, e.g., e-caprolactam (nylon-6), or of an amino carboxylic acid, e.g., 11 amino undecanoic acid (nylon-l1), or from interpolymers of these and other similar materials. Ordinarily the nylons employed for the practice of the instant invention are those obtained from reactants such as above described which yield linear polyamides having hydrogen bearing amide (NH) groups.

Importantly, the nylon filaments employed for the practice of the present invention are partly crystalline in structure, and preferably have been already stretch-oriented to the desired degree. The cross-linking treatment herein contemplated will, to a large extent, interfere with subsequent efforts to stretch orient the filament.

A principal object of the instant invention is to provide a novel cross-linked, crimped nylon filament.

A further object of the instant invention is to provide a chemical procedure for permanently crimping a nylon filament.

Briefly stated, the procedure of the instant invention involves first, asymmetric introduction of cross-links at the amide radicals in the polyamide molecules which make up the nylon filament to the total extent of from 1-50% of the amide hydrogen (NH). The linking radical must be longer than a simple methylene bridge and correspond at least to an ethylene chain in length. Irnportantly, the degree of cross-linking attained is asymmetric, i.e., not uniform across the cross-sectional area of the fiber. In effect a greater degree of cross-linking is attained on or near the peripheral surface of the filament than at the centermost regions thereof. Also the crystallites in the fiber are not severely cross-linked. Secondly, the cross-linked fiber is then swelled sufiiciently to achieve a volumetric change of from 2-20 times the volume of the initial unswelled filament. This swelling action will cause the fiber or filament to crimp to an extent consistent with the swelling agent employed, the character of the fiber and the degree of cross-linking effected. Lastly the swelling agent is removed and the filament dried. In its dry state the nylon filament so treated retains the crimp as a permanent characteristic.

The chemical nature of the cross-link and the manipulative procedures employed to eifect the differential crosslinking are subject to wide variations and there is no intent to restrict the instant invention to the specific crosslinking agents and procedures specifically set forth hereinafter by way of examples and preferred embodiments. Similarly the three steps above described, namely asymmetric partial cross-linking, solvent swelling, and removal of the swelling agents need not be practiced as three separate and discrete steps. Expressly contemplated isa procedure wherein the final step of the cross-linking sequence is effected in the presence of solvents which will at the same time swell the filament being cross-linked.

An essential aspect of the instant invention is employment of the chemically crimping procedure upon an already formed nylon crystalline filament. Once the filament has been prepared according to conventional practice, e.g., melt spun, stretch oriented to the desired degree, heat set, etc., with or without delustrants, e.g., titanium dioxide, it is suitable for practice of the instant invention. A filamentary nylorpwell adapted for practice of the instant invention is an undyed tow or skein of high tenacity nylon filament.

Indeed, the degree of crystallinity present in the nylon filament has such bearing upon the crimp attainable by a specific cross-linking and solvent swelling sequence that adjustment of the pre-imparted degree of crystallinity present in the nylon filament is an important parameter in the final qualities of the crimped cross-linked nylon filament which results from practice of the instant invention. For effective practice of the instant invention the filaments should have in excess of about 30% crystallites (vol. percent) therein. Other parameters are controls on the process itself and the chemical nature of the nylon filament. In passing it is noteworthy that the instant crimping procedure need not materially decrease the strength or stability of the nylon filament.

The degree of crimping possible with practice of the instant invention can vary from the merest twist to formation of helical coils, and the term crimp as used herein is intended to include also within its purview such physical effects as might be described by terms like: twist, bend, coil, etc.

Allusion has already been made as to how the various polyamide resins which as a class may be termed nylon can be cross-linked through the amide radical NH--. Ordinarily the amide hydrogen is itself replaced by a group of cross-linking radicals, but any already present substitute (i.e., NR) could be either converted into a cross-linking radical or replaced by one. However, the presence of substituents on the amide nitrogen other than hydrogen must be consistent, for practice of this invention with the physical limitation that the particular resin must somehow be formed into textile quality filaments, i.e., partly crystalline, often stretch oriented nylon filaments. Such filaments constitute the starting material for practice of the instant invention. Thus within quality limitation for nylon filaments process parameters can be suitably adjusted to compensate for composition variations such as for example the relative number of amide groups freely available for cross-linking purposes per unit molecular weight in the polyamide.

Some mention has already been made of the importance of elfecting the desired cross linking in an asymmetrical manner. To begin with it has been found that the crystallites remain virtually unaifected by the cross-linking reactions. Essentially therefore, the cross-linking reactions occur virtually entirely in the amorphous matrix in which the crystallites are embedded. Even in the amorphous polymer a substantial degree of asymmetry exists. The cross-linking reactions are deliberately not carried out to completion. As has been indicated only from 250% of the total number of the available amide groups in the filament are reacted. Since the cross-linking reaction is carried out on a macroscopic solid article, to wit, a filament, incomplete cross-linking necessarily results in a higher degree of substitution at or near the periphery of the filament than at the innermost portions thereof. In consequence the filament has been cross-linked to a highly asymmetric degree. In the amorphous polymer the level of cross-linking will vary from the mid point to the periphery; also randomly distributed throughout the filament cross section are virtually uncross-linked crystallite particles. As will be explained hereinafter, it is believed that this asymmetry of cross-linking creates physical stresses which result in the desired crimping when the asymmetrically cross-linked fiber is solvent swelled.

Particularly noteworthy however is that the cross-linking chain exceeds one methylene group in length. It has been found experimentally that one carbon cross-links, i.e. a methylene bridge does not result ultimately in the desired crimp.

The methylene bridge seems to form such a tight crosslink that the desired asymmetry cannot be readily produced and if produced prevents the solvation effect which causes crimping.

According to the detailed practice of the instant invention cross-linking is therefore effected on nylon filaments which have already been drawn and spun to the desired degree of orientation and crystallinity. In one exemplary technique a disulfide cross-linkage is formed according to the following reaction sequence:

t In still another exemplary reaction sequence an alkaline sulfide cross-linkage is formed according to the following:

E. I I

III-CHrS-CHr-S- O H2N (CH2)X2/ 0: (3:0 I (VI)' KSCH2-ITT Ty eA o=o p v IIIOITSCH'CHSCHIII oH20Hi X2\ I r 2- r I 0= 1 o=o v11) Type B where X :1 or Br, or Cl.

Step A involves the reaction of the amide hydrogen with the hemiacetal of formaldehyde and methylalcohol i in the presence of strong acids, producing an N-methoxymethylated polyamide (II). The structure of this product is established by actual N-methoxy analysis and by inference since polyamides prepared from N,N-alkylated diamines do not react with the hemiacetal of formaldehyde and rnethylalcohol. Also, infrared absorption spectroscopy indicates a substantial decrease in the intensity of certain 4 -NH absorption bands for the N-methoxymethylated polyamides.

The degree of N-substitution for cross-linking should range from about 150% of theoretical completeness at the amide groups, and preferably should be in the range of 530%. As a practical matter, the extreme portions of the 1-50% range are restricted to special conditions e.g. extreme crystallinity for the lower percentage and a virtual absence of crystallinity for the higher percentage. The presence of at least 20% (by volume X-ray or infrared measurement) crystallites is important to practice of the instant invention.

In the experimental work from which thebelow given examples are taken, the N-methoxyrnethylation of solid nylon-6 fiber was carried through to formation of 3 to 4% methoxy groups (depending on the experimental conditions used) which corresponds to an amide substitution in the polymer of approximately 10-15%. X-ray diffraction patterns of the N-methoxymethylated and unmodified fibers show little change of crystallinity, indicating that only the amorphous regions were penetrated by the reagents. Since the nylon-6' fiber used was about 50% crystalline, 2030% of the amide groups in the amorphous regions of the polymer were methoxy methylated.

Steps B and C involve the reaction of the methoxy methylated fiber with thiourea in the presence of strong acids and subsequent treatment with alkali to yield the sulfhydril product (IV). Alternatively, the methoxylated fiber could be reacted with thioacetamide in the presence of methyl alcohol (as swelling agent) and concentrated hydrochloric acid.

To determine the effect of the reaction medium on the extent of reactions A, B and C, experiments were carried out both in Water and in methyl alcohol, respectively (the latter being a plasticizer for N-rnethoxymethylated polyamides). In the experiments in water, methoxymethylated nylon-6 fibers were treated with thiourea and hydrochloric acid under various conditions, and then reacted with potassium hydroxide with concurrent rapid air-oxidation. Thus, the final filament contained both sulfhydril groups and disulfide cross-links.

In the corresponding series of experiments Where methyl alcohol was chosen as the reaction medium, the plasticizing effect of this solvent on N-methoxymethylated polya mides facilitated the opening of the amorphous regions with some decrease in the crystallinity of the fiber. (The experiments were carried out at room temperature since hot methyl alcohol partially dissolves the methoxymethylated fiber.)

A substantial increase in sulfur content resulted from the methanol reaction medium over the reactions which had been carried out in water.

' In lieu of oxidizing the sulfhydrate (IV), the potas- II CN-CH2S(CH2)nX where n=1 or 2, and X :1 or Br, or C1. The presence of these latter groups could be expected since, because of steric factors, not all potassium mercaptide groups can form cross-links and, therefore, are subject only to the blocking reaction. However, no significant amounts of free potassium mercaptide or sulfhydn'l groups were detected in the alkylene sulfide cross-linked fibers by a sensitive technique, specially devised for this purpose.

The swelled disulfide cross-linked nylon-6 fibers exhibited three-dimensional wavy crimping of uneven distribution and dimensions, both in the wet and dry states, similar to wool. This crimping was especially pronounced.

in those fibers which had been treated in the presence of methyl alcohol and cross-linked by either rapid air oxidation or by dilute solutions of H 0 for 30 minutes. Much reduced, but still noticeable crimping was also exhibited by those samples which had been cross linked in the presence of water instead of methyl alcohol. The

more pronounced crimp of helical coiling was produced by either series of fibers when they were treated with m-cresol (a solvent which destroyed the remaining crystallites The alkylene sulfide cross-linked nylon-6 homofilaments exhibited self-crimping of uneven distribution and dimensions in both dry and water wet states similar to those of the disulfide cross-linked fibers. However, these macroscopic crimp deformations differed in at least three respects from those of the disulfide cross-linked samples: (1) the crimp frequency was much higher and the crimpamplitude smaller, (2) an extreme crimping i.e. some helical coiling occurred even when the fiber was in the unswollen state, and (3) the extent of crimping was not gradually decreased by air-oxidation of unreacted sulfhydril groups.

Without being bound thereto it is believed that the crimping effect can be explained by the asymmetric inhomogeneity of the cross-linking. Allusion has' already been made to how the crystallites are not, by and large, methoxylated and as a result do not become cross-linked to the extent which the amorphous portions of the fiber are cross linked. Mention also has been made that the cross-linking of the amorphous portions is not complete and how almost of necessity, the degree of cross linking varies throughout the amorphous resin in the fiber crosssection, being greatest nearest the outside surfaces and being proportionately least at the innermost regions of the filament. However, some cross linking should occur even at the innermost portions of the filament. In the instance of cross-linking through disulfide cross-links, the final oxidation to the cross-linking disulfide was brought about either by rapid air oxidation or by a brief treatment with dilute solutions of hydrogen peroxide. It is reasonable to believe that this treatment will oxidize the sulfhydril groups located near to the surface of the fiber to a greater extent than those situated toward the center. Furthermore, onset of oxidation will be accelerated at points along the fiber axis which are more easily penetrated. Inasmuch as the cross-linking reactions are not really carried to actual completion there results a substan tial asymmetry of the various cross-linking density across the fiber cross-section. Even though the fiber is crosslinked throughout it has an outer portion with a higher degree of cross-linking, an inside portion with fewer cross links, and in addition scattered throughout the fiber volume essentially uncross-linked crystallites.

In consequence of this asymmetry, solvating the fiber filament by contact with a solvent capable of swelling the filament as a whole to at least twice its original volume will cause differential swelling at microscopic sized portions of the filament. The least cross-linked amorphous portion will swell more than the more crosslinked portions; in good solvents the crystallites themselves will be solvated. In total, internal stresses arise which cause the swelled fiber to crimp. The degree of crimping which results can be related to the solvating effect of the solvent.

The crimp so attained is permanent, remaining when the solvent is removed and the filament dried.

The foregoing explanation is consistent with the experimental tests wherein the cross-linked fiber was treated with a poor solvent, i.e., water, capable of swelling only the amorphous, least cross-linked portions of the fiber, but not the crystallites. Little or no deformation occurs. Apparently the internal forces which tend to deform and crimp the fiber are opposed by the crystallites in the fiber. The relatively small differential swelling in water is insuflicient to overcome the dimensionally stabilizing effect of the crystallites which remain dominant, particularly in the instances where the particular fiber employed during the test was approximately 50% crystalline. The small degree of crimping which, however, did occur shows what substantial internal forces are involved.

On the other hand, when a very good solvent (specifically m-cresol) was employed, complete destruction of the crystallites was effected and as a result of solvation the fiber deformed to the extent of helical coils.

For actual practice of the instant invention, it is contempleted that other swelling agents besides m-cresol or water would be employed judiciously in order to achieve a desired level of crimping with the least effect on the crystallinity of the fiber. Suitable swelling agents are the 1-4 carbon alcohols, their acetates, benzylalcohol, etc.

Still further tests tend to corroborate the above proposed explanation of why the instant procedure effects crimping. These tests also indicate that cross-linking the fibers throughout, not only near the surface, is significant. Tests were made in which cross-linking was deliberately restricted to near the surface areas; the resulting fibers when treated with swelling agents (m-cresol) capable of dissolving the uncross-linked structure, produced merely a hole in the middle of the fiber. In these fibers no crimping was observed, apparently because virtually no differential swelling occurred.

Similarly, the existence and importance of differential swelling was demonstrated in the case of the disulfide cross-linked fiber by a test on the already cross-linked fibers, wherein the final oxidation was extended by more prolonged oxidation with dilute hydrogen peroxide, whereby the filaments exhibited a greatly diminished crimping tendency. The result, most likely, is due to the more uniform distribution of the cross-links throughout the filament achieved by virtue of better penetration of the oxidizing agent.

Still additional corroboration appeared in the experimental Work directed to the introduction of alkylene sulfide cross links. Some disulfide cross-links apparently were formed due to partial air oxidation of the mercaptide groups during the handling of the filaments. These crosslinks appear to exercise a localized restraining effect upon the amorphous structure since some crimping resulted during the mild swelling which occurred during the washing and handling of the mercaptide fiber. Also since the subsequent cross-linking step actually involves simultaneously (l) swelling of the fiber in a mixture of benzyl alcohol and ethyl alcohol and (2) additional cross-linking through formation of the alkalene sulfide groups, a continuing swelling and internal plasticization of the fiber ocours with partial disruption of the crystallites gradually taking place during penetration of the alkylene dihalide reagent throughout the fiber. Initially as the crystallites are disrupted some of this resistance is removed; the crimping becomes more pronounced. Introduction of further alkylene sulfide cross-links when the fiber is in the thusly deformed state creates a tendency to reinforce the deformation and accentuate the extent of crimping. If later complete destruction of the crystallites is permitted (as occurs by swelling in m-cresol) the fiber crimps further, helically coiling; apparently then all counterforce to deformation has been removed.

Still further corroboration is available in the X-ray data. An oriented highly crystalline fiber filament cn'mped by both the alkylene sulfide and the disulfide cross-link exhibited virtually the same degree of crystallinity, but a lesser degree of orientation than the untreated filament. This result is consistent with the existence of differential swelling when the fiber is solvated and is attributable to relative displacement of the crystallites, decreasing thereby the orientation.

In passing'it is noteworthy that the disulfide product can largely be converted to an alkylene sulfide cross-link (CH S-S-CH CH -SCH by heating the disulfided material to nearly the softening point of the filament. As a point of preference the alkyleue sulfide cross-link is considered superior since the end product is more stable. Also subsequent treatment to block free sulfhydril groups, as for example with silver nitrate, is not necessary.

For further understanding of the instant invention reference is now made to the following examples.

Example l.N-melhoxymethylation Step A A small skein of semi-dull 70/ 32 denier nylon-6 fiber, weighing approximately 0.1-0.2 gram was scoured for 30 minutes in water containing 1-2% Na PO washed in distilled water and dried.

A solution was prepared containing 500 grams of paraformaldehyde and 500 grams (625 ml.) methyl alcohol by heating the solution to 60 C. and adding 3-4 pellets of KOH. The solution was stirred at this temperature until all paraformaldehyde dissolved (approx. 15 minutes) and then it was allowed to cool to room temperature. The pH of the solution was then adjusted to 0.6-0.7 with anhydrous oxalic acid (approximately 40 grams). The skein was soaked in this solution for 12 hours at room temperature after which it was removed from the bath and heated at 120 C. in a closed oven for one minute, rinsed in methyl alcohol, water, and dried. Methoxy analysis: 3.4%.

Example II.Intrducti0n of sulfhydril group and oxidation to disulfide cross-links Steps B, C, and D Run N 0. 1.The N-met'hoxymethylated nylon-6 fiber 1 was soaked in a solution containing 38.0 grams thiourea (0.5 mole), 700 ml. distilled water and 35 ml. conc. HCl (0.42 mole) at room temperature for 12 hours. After this period 28.0 grams (0.5 mole) of KOH was added in 100 ml. distilled water and the fiber was permitted to soak at room temperature for 12 hours with concurrent airoxidation from a porous-disc bubbler. Next, the fiber was removed from the solution, thoroughly washed with distilled water and dried. S=2.1%.

Run N0. 2.Same as above, except that fiber was soaked for one hour in the thiourea, H 0, and HCl mixture and for one hour in KOH. S=1.0%.

Run N 0. 3.The N-methoxymethylated nylon-6 fiber 1 was soaked in a solution containing 38.0 grams thiourea (0.5 mole) and 700 ml. distilled water for 12 hours at room temperature. Next, 25 ml. of cone. HCl (0.42 mole) was added and the fiber soaked for one hour at room temperature. After this period 28.0 grams (0.5 mole) of KOH was added in 100 ml. distilled water and the fiber was permitted to soak at room temperature for one hour with concurrent air-oxidation from a porous-disc bubbler. The fiber was then Washed with distilled water and dried.

Run N0. .4.The N-methoxymethylated nylon-6 fiber 1 was soaked in a solution containing 38.0 grams thiourea (0.5 mole) and 700 ml. distilled water for 2 hours at 60 C. The solution was cooled to room temperature and then 28.0 grams (0.5 mole) of KOH was added in 100 ml. distilled water, the fiber was soaked in this solution for one hour at room temperature with concurrent air-oxidation from a porous-disc bubbler. The fiber was then washed with distilled water and dried. S=l.0%.

The following table shows the analytical data on the products of Runs 1-4 including solvating effect of water, the dry condition and the effect of subsequent solvation with m-cresol.

1 N-methoxymethylated nylon-6: 3.4% methoxy groups.

ANALYTICAL DATA ON STRUCTURALLY MODIFIED.

NYLON-6 FIBERS (WATER USED AS REACTION MEDIUM) Amide Sub- Comments Run Total, e stitution, qm b No. Percent Percent Dry orWet m-Oresol (Water) 1 2.1 7.4 11.7 Very few Helix.

crimps. 2 1.0 3.6 14.4 do.- Do. 3 1.3 4.8 6.9 do Do. 4 1.0 3.6 8.5 0 D0.

1irikTotal sulfur includes both sulfhydril groups and disulfide crossages.

b Measured photomierographieally after 24 hrs. air-oxidation, qm; V/Vo, where V=volume of network at swelling equilibrium in m-eresol and Vo=volume of network before swelling:

Run N0. 5.Same as Run No. 1, except that methyl NYLON-6 FIBERS (METHYL ALCOHOL USED AS REAC- TION MEDIUM) Amide Comments Run Total S Substituqm N0. tion Dry or Wet m-Cresol 2 9 .3 6 7 Highly Helix.

crimped 3.5 12.4 3.4 0 D0. 2.7 9.5 4.3 ..do D0.

li kTotal sulfur includes both sylfhydril groups and disulfide crossn ages.

b Measured photomicrographieally after 24 hrs. air-oxidation, qm= V/Vo, where V=volume of network at equilibrium swelling, Vo=v0lume of network before swelling.

Example III.--Oxidalion of sulfhydril groups to disulfide linkages with H 0 To determine the effect of further oxidation the skeins from Runs 1 to 7, respectively, were soaked at room temperature in a solution consisting of 250 ml. distilled water, 2 pellets of KOH and 10 ml. of 3% H 0 for 30 minutes to 4 hours, depending on the particular experiment. The following table shows to what an extent the cross-linking is increased as measured by the decrease in swelling when solvated by m-cresol.

EQUILIBRIUM VOLUME SWELLING RATIOS 1 OF SAMPLES OXIDIZED BY AIR AND HYDROGEN PEROXIDE Sample No. (Run) Air24hr.,qm H m-30 HgO2-4 Im'n., qm hr., qm

1 Measured photornierographically, qm=V/Vu, where V=volume of network at equilibrium swelling, Vu=volume of network before swelling Example IV V 'In this example all work was carried out with 7.8 Tex. (60 denier) 32 filament round cross-section nylon-6 I homofiber.

Step 1N-meflz0xymethylation.This reaction was. carried out according to the procedure of Example I.

Step 2Preparati0n of the mercapzides (F) Exp. N0. 1, Table IV.A small skein (0.1-0.2 gram) of the N- methoxymethylated nylon-6 fiber was soaked for 12 hours at room temperature in a solution containing 37.5 grams (0.5 mole) of thioacetamide and 700 ml. of methyl alcohol. Next, 35 ml. of cone. HCl (0.42 mole) was added and the fiber soaked for one hour at room temperature. After this period 60.0 grams (1.06 moles) of KOH was added to 200 ml. of methyl alcohol and the fiber was permitted to soak at room temperature for one hour. The fiber was then washed thoroughly twice with methyl alcohol, twice with distilled water, and again twice with methyl alcohol.

Step 3-Intr0ducti0n of Type A alkylene sulfide crosslinkages, Exp. No. 1, Table IV.(a) The fiber from (2) was soaked for 5 hours at room temperature in a solution of 150 ml. of ethyl alcohol, 150 ml. of benzyl alcoho], and 29 ml. (0.36 mole) of ethylene diiodide. After this period the sample was thoroughly washed twice with ethyl alcohol, twice with distilled water, and twice with methyl alcohol and allowed to dry at room temperature. S=3.7%

(b) The procedure was the same as in (a), except that soaking time was 24 hours instead of 5 hours, (Exp. No. 2, Table IV). S=3.6%.

Step 3AIntroduction of Type B alkylene sulfide crosslinkages, Exp. Nos. 3 and 4, Table IV.The fiber from (2) was soaked for 24 hours at room temperature in a solution of 90 ml. of ethyl alcohol, 90 ml. of benzyl alcohol, and 90 ml. (1.04 moles) of 1,2-dibromoetl1ane. After this period the sample was thoroughly washed twice with ethyl alcohol, twice with distilled water, and twice with methyl alcohol, and allowed to dry at room temperature. S=2.0%.

Step 3BIntr0ducti0n of disulfide cross-links (E), Exp. No. 5, Table 1V.This reaction was carried out according to the procedure of Example 2. S=2.7%.

ANALYTICAL DATA ON CROSS-LINKED NYLON-6 FIBERS Example V Skeins of 3 denier filament of nylon-11 and 66 were asymmetrically partially cross-linked according to the procedure set forth in Example IV to produce both Type A alkylene sulfide and Type B alkylene sulfide cross-linking.

The resulting swelling ratios were not measured exactly, but for nylon-66 appeared about the same as for nylon-6, and about 50% greater for nylon-11. The degree of crimping was considerably less for the nylon-66 as for nylon-6, and even less for nylon-11.

While the examples have shown the practice of the invention in terms of disulfide and alkylene sulfide crosslinking bonds, it should be understood that other crosslinking chains might be employed with or without completely difi'erent cross-linking procedures. Thus for example irradiation of the filament with high voltage electron beams might be employed in suitable cross-linking procedures to form a cross-link of at least the length of an ethylene chain. Many different embodiments of this invention may be made without departing from the spirit and scope thereof, as defined in the appended claims.

What is claimed is:

1. A procedure for crimping nylon filaments which comprises asymmetrically incompletely cross-linking filamentary nylon through the amide NH radical to the extent of from 25 0% of the theoretically available amide groups, said nylon having at least 20% by volume thereof of crystallites, the cross-linking being effected by methoxy methylating the nylon, thereafter sulfiding the methoxymethylate, then cross-linking through the resulting sulfide, solvating the filamentary nylon to a volume thereof at least twice the initial filament volume, and thereafter drying the filamentary nylon.

2. The process of claim 1 wherein a disulfide crosslink is formed.

3. The process of claim 1 wherein an alkylene sulfide cross-link is formed in the presence of a solvent whereby the filamentary nylon self crimps as it is being cross-linked and swelled, and thereafter drying the crimped crosslinked filamentary nylon.

References Cited UNITED STATES PATENTS OTHER REFERENCES Chem. Abstracts, vol. 46, p. 8859g (1952), Abstract of Watanabe article appearing vol. 8, pp. 220-224 (1952).

Chem. Abstracts, Vol. 47, p. 250313 (1953), Abstract of the Noishiki et al. Japanese Patent No. 4,273 of Aug. 2, 1951.

NORMAN G. TORCHIN, Primary Examiner.

J. TRAVIS BROWN, DONALD W. PARKER,

Examiners.

J. C. CANNON, A. J. SMEDEROVAC,

Assistant Examiners. 

1. A PROCEDURE FOR CRIMPING NYLON FILAMENTS WHICH COMPRISES ASYMMETRICALLY INCOMPLETELY CROSS-LINKING FILAMENTARY NYLON THROUGH THE AMIDE - NH- RADICAL TO THE EXTENT OF FROM 2-50% OF THE THEORETCALLY AVAILABLE AMIDE GROUPS, SAID NYLON HAVING AT LEAST 20% BY VOLUME THEREOF OF CRYSTALLITES, THE CROSS-LINKING BEING EFFECTED BY METHOXY METHYLATING THE NYLON, THEREAFTER SULFIDING THE METHOXYMETHYLATE, THE CROSS-LINKING THROUGH THE RESULTING SULFIDE, SOLVATING THE FILAMENTARY NYLON TO A VOLUME THEREOF AT LEAST TWICE THE INITIAL FILAMENT VOLUME, AND THEREAFTER DRYING THE FILAMENTARY NYLON. 